Regulators are widely used to isolate a power supply and load. They are generally of two types: (1) regulators intended to insure constant load voltage or current independent of power supply fluctuations, or (2) regulators intended to insure constant power supply voltage or current independent of load variations. Some equipment may employ both types of regulators.
The second type of regulator is particularly important where it is desired to prevent multiple loads sharing a common power supply from interfering with each other, as for example, fluctuations in one load being coupled back to the power supply where they may affect the voltage or current being supplied to another load.
Another application in which the second type of regulator is important is in connection with equipment where a high degree of data security is desired. For example, if fluctuations in the data being processed by the load cause fluctuations in the power supply current or voltage, these power supply fluctuations may be susceptible to external detection and therefore compromise data security. For instance, if the load is a communication processor handling digital or analog data, where the data manipulation by the processor causes the load impedance seen by the power supply to fluctuate in a manner correlated with the data, then the fluctuating current drawn from the power supply and/or fluctuating power supply voltage can contain information correlated with the data. By monitoring the supply lines from the power supply to the load, or even just the input lines from the mains to the power supply, the digital or analog information being handled by the load may be detectable. A further risk in this situation is that the Power supply fluctuations may radiate and be detectable from a considerable distance from the apparatus without any direct connection thereto.
Where a high degree of data security is important, it is desirable that the power supply run at substantially constant voltage and/or constant current (or both), despite fluctuations of load impedance and corresponding load current and/or voltage fluctuations. It is not necessary that all power supply fluctuations be suppressed, but only those fluctuations that would correlate with the data. These data related fluctuations in the load current or voltage can be viewed as an AC noise created by the load which it is desirable to prevent being coupled to the power supply. Slow (near DC) fluctuations in the load current or voltage can generally be tolerated since even though coupled to the power supply, they contain little or no significant information about the data being processed by the load. When the AC load fluctuations are suppressed or compensated, monitoring the power supply does not give information on the data being processed by the load.
While many regulator circuits are known in the art, they suffer from a number of limitations, as for example, excessive power consumption, especially under stand-by conditions. Further, while it is known to provide isolation between power supply and load by using LC filters to remove or block out high frequency load induced transients, this is not practical in many applications when the frequency of the transients is such that the required inductors (L) and capacitors (C) are too large and too heavy.
Thus, an ongoing need continues to exist for an improved means and method for regulators, especially AC regulators which isolate the power supply from the load with a high degree of effectiveness. It is further desirable that the regulator consume as little power as possible when not regulating, e.g., during stand-by, since available power is at a premium in many applications, as for example, in hand-held and battery operated equipment. It is still further desirable that the isolation be accomplished over a broad frequency range without use of bulky filter capacitors and inductors.